docs: def get_ceph_df(self, sentry_unit):
          """Return dict of ceph df json output, including ceph pool state.
  
          :param sentry_unit: Pointer to amulet sentry instance (juju unit)
          :returns: Dict of ceph df output
          """
          cmd = 'sudo ceph df --format=json'
          output, code = sentry_unit.run(cmd)
          if code != 0:
              msg = ('{} `{}` returned {} '
                     '{}'.format(sentry_unit.info['unit_name'],
                                 cmd, code, output))
              amulet.raise_status(amulet.FAIL, msg=msg)
          return json.loads(output)